Progress in extending high poloidal beta scenarios on DIII-D towards a steady-state fusion reactor and impact of energetic particles Articles uri icon

authors

  • Huang, J.
  • Garofalo, A. M.
  • Qian, J. P.
  • Gong, X. Z.
  • Ding, S. Y.
  • VARELA RODRIGUEZ, JACOBO
  • Chen, J. L.
  • Guo, W. F.
  • Li, K.
  • Wu, M. Q.
  • Pan, C. K.
  • Ren, Q.
  • Zhang, B.
  • Lao, L. L.
  • Holcomb, C. T.
  • McClenaghan, J.
  • Weisberg, D.
  • Chan, V.
  • Hyatt, A.
  • Hu, W. H.
  • Li, G. Q.
  • Ferron, J.
  • McKee, G.
  • Pinsker, R. I.
  • Rhodes, T.
  • Staebler, G. M.
  • Spong, D.
  • Yan, Z.

publication date

  • September 2020

start page

  • 1

end page

  • 12

issue

  • 12, 126007

volume

  • 60

International Standard Serial Number (ISSN)

  • 0029-5515

Electronic International Standard Serial Number (EISSN)

  • 1741-4326

abstract

  • To prepare for steady-state operation of future fusion reactors (e.g. the International Thermonuclear Experimental Reactor and China Fusion Engineering Test Reactor (CFETR)), experiments on DIII-D have extended the high poloidal beta (βP) scenario to reactor-relevant edge safety factor q95 ~ 6.0, while maintaining a large-radius internal transport barrier (ITB) using negative magnetic shear. Excellent energy confinement quality (H98y2 > 1.5) is sustained at high normalized beta (βN ~ 3.5). This high-performance ITB state with Greenwald density fraction near 100% and qmin ≥ 3 is achieved with toroidal plasma rotation Vtor ~ 0 at ρ ≥ 0.6. This is a key result for reactors expected to have low Vtor. At high βP (≥1.9), large Shafranov shift can stabilize turbulence leading to a high confinement state with a low pedestal and an ITB. At lower βP (<1.9), negative magnetic shear in the plasma core contributes to turbulence suppression and can compensate for reduced Shafranov shift to continue to access a large-radius ITB and excellent confinement with low Vtor, consistent with the results of gyrofluid transport simulations. These high-βP cases are characterized by weak/no Alfvén eigenmodes (a.e.) and classical fast-ion transport. At high density, the fast-ion deceleration time decreases and ∆βfast is lower; these reduce a.e. drive. The reverse-shear Alfv´en eigenmodes are weaker or stable because the negative magnetic shear region is located at higher radius, away from the peaked fast-ion profile. Resistive wall modes can be a limitation at simultaneous high βN, low internal inductance, and low rotation. Analysis suggests that additional off-axis external current drive could provide a more stable path at reduced q95. Based on a DIII-D high-βP plasma with large-radius ITB, two scenarios are proposed for CFETR Q = 5 steady-state operation with ~1 GW fusion power: a lower-li (li ~ 0.66) and a higher-li (li ~ 0.75) case. Using a Landau closure model, multiple energetic particle (EP) effects on the a.e. stability are analyzed modifying the growth rate of the a.e.s triggered by the neutral-beam-injection EPs and alpha particles, although the stabilizing/destabilizing effect is weak for the cases analyzed. The stabilizing effects of the combined EP species β, energy, and density profile in CFETR need further investigation.

keywords

  • energetic particle; high bootstrap current; steady state; tokamak